The ability to identify suitable food substances and avoid dangerous ones is imperative to survival in the animal kingdom. Information about satisfactory food substances is mediated by chemoreceptors designed to bind specific chemical compounds in food substances. Chemoreceptors involved in food detection are not only highly specific to chemical compounds, but also, for obvious reasons, distinct between species. Because of this high specificity, each species may miss out on potential food sources but is able to target energy on a subset of viable food sources (Garrity et al., 2011).

Even more important to survival than identification of suitable food sources is avoidance of harmful substances. Little is known about the chemoreceptive mechanisms that prevent ingestion of noxious stimuli. Unlike positive food source identification, which can be tailored and narrow, receptors designed to prevent consumption of noxious stimuli must be able to detect a wide range of potentially damaging substances. Wang et al. (2011) demonstrated that avoidance of noxious stimuli may be communicated via channels that detect broad characteristics of chemical compounds, such as weak acidity, or electrophilicity.

TRPA1 is one such receptor that detects weak acids and  may be involved in attenuation of feeding behavior in Drosophila. The lab of Paul Garrity explored the mechanism of action of TRPA1 channels in Drosophila in relation to a stereotyped feeding behavior, the proboscis extension response (PER). Drosophila exhibit this behavior when their legs come in contact with a food source, such as sucrose. Kang et al. discovered that PER was drastically decreased when flies were exposed to food sources containing reactive electrophiles. In TrpA1 loss of function mutants, the attenuation of PER in response to reactive electrophiles was drastically decreased, suggesting a role for TRPA1 in preventing ingestion of noxious stimuli. RNAi experiments conducted as part of the same study showed that TRPA1 expression in the neurons innervating the labral sensory organ sensilla no. 8 and 9 is necessary for preventing the ingestion of unfit food sources (Kang et al., 2010).

Image

Figure 1 – dTrpA1 mediates gustatory response to reactive electrophiles
a, Chemical structures. b, Proboscis extension response (PER) frequency at five sequential tastant offerings, ingestion permitted. (*p<0.05, **p<0.01, unpaired t-test.) c, PER, tastant contacts only legs. Five sequential offerings combined (n≥10 flies). d, PER, ingestion permitted: light blue, first offering; dark blue, second to fifth offerings combined. Statistically distinct groups marked by different letters (Tukey HSD, α=0.01). Data are mean +/− SEM. All studies use 12% (350mM) sucrose, alone or with 100 mM caffeine, 2 mM AITC, 10 mM NMM, or 6 mM CA. n=3 groups of ≥7 flies, unless noted. From Kang et al, 2010.

The authors suggest that TRPA1, and other channels like it, may be mediating the widespread aversion in the animal kingdom to ingestion of noxious stimuli, such as reactive electrophiles. Despite the evolutionary conservation of this gene, differences in thermal and nicotinic responses in TRPA1 exist across species. In light of this, targeted TRPA1 agonists may be useful in the elimination of pests, without causing harm to humans and other animals.

Please join us for the third installment of the 2012-2013 Neuroscience Seminar Series at 4 pm on Tuesday, October 9th in the CNBC Large Conference Room, as Paul Garrity shares his insights about TRPA1 and its evolutionary history.

Paul Garrity: Overheated and rather irritated: TRPA1 and the evolution of thermal and chemical sensing

Cailey Bromer is a first year in the Neuroscience PhD program. She is completing her fall rotation with Dr. John Kelsoe.


Kang K., Pulver S.R., Panzano V.C., Chang E.C., Griffith L.C., Theobald D.L. & Garrity P.A. (2010). Analysis of Drosophila TRPA1 reveals an ancient origin for human chemical nociception, Nature, 464 (7288) 597-600. DOI:

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s